The term “front-end” as used in this disclosure, means the components and functions between the antennas and the power amplifiers or RF-ASIC (radio frequency application specific integrated circuit), but some front-end modules may also include power amplifiers. The front-end in multiband, multimode engines, especially those that are designed to meet the requirement of MIMO (multiple-input, multiple-output) and/or diversity functionality, is usually very complex in construction and design. Because the front-end generally comprises many switches, it consumes a significant amount of electrical current and needs many control lines. MIMO functionality is required in new and future mobile terminals and, initially, Rx MIMO is prioritized because the downlink data rate is more important than the uplink counterpart in mobile communications. Essentially, Rx MIMO requires more than one Rx path to be provided on a particular band of operations. The outputs of these paths are then monitored and combined to give an enhanced data rate. The antenna feed to each of these paths is independent from each other.
Currently, a GSM/W-CDMA multimode engine is designed to have a separate GSM antenna and a separate W-CDMA antenna. A W-CDMA antenna is connected to a duplexer that has a passband filter for both the Rx and Tx paths of the W-CDMA mode. The GSM antenna is connected to an antenna switch module that typically first separates the 1 GHz frequencies from the 2 GHz bands using a diplexer or the like. The Rx and Tx paths of each frequency range are then separated by switches. The antenna switch module often also includes harmonic filtering for the power amplifier outputs and may include surface-acoustic wave (SAW) filters to provide filtering for the Rx paths. A typical block diagram of a typical front-end is shown in FIGS. 1a and 1b. As shown in FIG. 1a, the GSM module includes four sections: 1 GHz GSM Rx section, 1 GHz GSM Tx section, 2 GHz GSM Rx section and 2 GHz GSM Tx section. The 1 GHz GSM Rx section includes an 869-894 MHz Rx path 110, and the 925-960 MHz Rx path 130. The 1 GHz GSM Tx section, collectively denoted as path 150, includes two frequency bands of 824-849 MHz and 880-905 MHz. The 869-894 MHz Rx path 110 includes a filter 116 connected between ports 112 and a balun 122. The 925-960 MHz Rx path 130 includes a filter 136 connected between ports 132 and a balun 142. The balun functionality can be incorporated into the filters 116 & 136 depending on the filter technology. The Rx paths 110 and 130 are joined at a common node 410. These Rx paths are also joined with the port 152 of the 824 -849/880-905 MHz Tx path 150 at a node 412 via a matching element 80. Here PIN diodes 42 and 44 are used for Tx-Rx switching. Alternatively, other switch technologies can be also used e.g. CMOS or GaAs p-HEMTs (Pseudomorphic High Electron Mobility Transistor). However, by using the CMOS and p-HEMT switches, the arrangement of biasing and matching elements will be slightly modified.
The 2 GHZ Rx section includes a 1805-1880 MHz Rx path 220, commonly referred to as the 1800 GSM mode, and the 1930 -1990 MHz Rx path 240, commonly referred to as the 1900 GSM mode. The 2 GHz GSM Tx section, collectively denoted as path 260, includes two frequency bands of 1710-1758 MHz and 1850-1910 MHz. The 1805-1880 MHz Rx path 220 includes a filter 226 connected between ports 222 and a balun 232. The 1930-1990 MHz Rx path 240 includes a filter 246 connected between ports 242 and a balun 252. The Rx paths 220 and 240 are joined at a common node 414 with matching circuits or devices 84, 86. These Rx paths are also joined with the port 262 of the 1710 -1758/1850-1910 MHz Tx path 260 at a node 416 via a matching element 82. Here PIN diodes 46, 48 are used for Tx-Rx switching. The 1 GHz and 2 GHZ parts are connected to a common feed point 418 of the GSM antenna 10 through a diplexer 30, which comprises harmonic filters 32, 34 for the Tx paths 150 and 260.
In FIG. 1b, the W-CDMA module has two paths: a 2110-2170 MHz Rx path 320 and a 1920-1980 MHz Tx path 340. The Rx path 320 includes a filter 326 connected between ports 322 and a balun 332. However, the balun can also be after the filter and external to the duplexer. The 1920-1980 Tx path 340 has a passband filter 346 and a port 342. The Rx path 320 is joined with the Tx path 340 at a node 420 and a common W-CDMA antenna 20 via a matching element 90.
To use one antenna for the GSM mode and one antenna for the W-CDMA mode, it is required that the front-end includes matching devices 80, 82, 84, 86 and other necessary components for matching and biasing, depending also on the switch technology chosen, to separate the 1805-1880 MHz GSM Rx path 220 and the 1930-1990 MHz GSM Rx path 240. The front-end architecture is complex and the additional losses in these reception paths occur.
It is advantageous and desirable to provide a front-end architecture where the complexity can be reduced.